They told him to shut up and go home.
You are probably aware that a lot of people who don't really know what they're talking about keep saying that the Large Hadron Collider is going to devour everything (literally - everything) in a black hole.
It was everywhere just a few weeks ago when they were getting ready to power up the LHC to test it. Even in the grocery store I heard people talking about it. I resisted the urge to yell at them. Barely.
Scientists have said a lot about this. For instance, that the LHC doesn't have nearly the amount of power to create a black hole. Even if it did, such a black hole would be incredibly unstable and instantaneously vanish in a puff of Hawking radiation. Even if all that didn't happen, it would be so small that our sun would have turned into a red giant and obliterated the solar system well before the black hole could devour a single gram of matter.
The probability of this being an actual threat has been compared to the probability of your car spontaneously turning into a horse due to random quantum fluctuations.
What the LHC is likely to do is answer a lot of our questions about physics, and it will lead to incredibly advances in our technology. The LHC puts out over a gigabyte of data per second. Scientists created a new thing called the Grid to deal with that. Wonder if that'll find its way into the world at large.